EMC2303-1-KP-TR Standard Microsystems (SMSC), EMC2303-1-KP-TR Datasheet - Page 19

• Manufacturer Part Number: EMC2303-1-KP-TR
• Manufacturer: Standard Microsystems (SMSC)

Specifications of EMC2303-1-KP-TR

• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (min): 3V
• Operating Supply Voltage (max): 3.6V
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• Mounting: Surface Mount
• Pin Count: 12
• Lead Free Status / RoHS Status: Compliant

Multiple RPM-Based PWM Fan Controller for Three Fans
Datasheet
APPLICATION NOTE: The tachometer measurement method works independently of the drive settings. If the
SMSC EMC2303
4.3.1
4.4
4.4.1
The EMC2303’s RPM-based Fan Speed Control Algorithm has programmable configuration settings
for parameters such as ramp-rate control and spin up conditions. The fan driver automatically detects
and attempts to alleviate a stalled/stuck fan condition while also asserting the ALERT# pin. The
EMC2303 works with fans that operate up to 16,000 RPMs and provide a valid tachometer signal.
The fan controller will function either with an externally supplied 32.768kHz clock source or with it’s
own internal 32kHz oscillator depending on the required accuracy. The EMC2303 offers a clock output
that enables additional devices to be slaved to the same clock source.
Programming the RPM-based Fan Speed Control Algorithm
The RPM-based Fan Speed Control Algorithm is disabled upon device power up. The following
registers control the algorithm. The EMC2303 fan control registers are pre-loaded with defaults that
will work for a wide variety of fans so only the TACH Target Register is required to set a fan speed.
The other fan control registers can be used to fine-tune the algorithm behavior based on application
requirements.
Note that steps 1 - 6 are optional and need only be performed if the default settings do not provide
the desired fan response.
1. Set the Spin Up Configuration Register to the Spin Up Level and Spin Time desired.
2. Set the Fan Step Register to the desired step size.
3. Set the Fan Minimum Drive Register to the minimum drive value that will maintain fan operation.
4. Set the Update Time and Edges options in the Fan Configuration Register.
5. Set the Valid TACH Count Register to the highest tach count that indicates the fan is spinning.
6. Set the TACH Target Register to the desired tachometer count.
7. Enable the RPM-based Fan Speed Control Algorithm by setting the EN_ALGO bit.
The tachometer measurement circuitry is used in conjunction with the RPM-based Fan Speed Control
Algorithm to update the fan driver output. Additionally, it can be used in Direct Setting mode as a
diagnostic for host based fan control.
This method monitors the TACHx signal in real time. It constantly updates the tachometer
measurement by reporting the number of clocks between a user programmed number of edges on the
TACHx signal (see
The tachometer measurement provides fast response times for the RPM-based Fan Speed Control
Algorithm and the data is presented as a count value that represents the fan RPM period.
Stalled Fan
A Stalled fan is detected if the tach counter exceeds the user-programmable Valid TACH Count setting.
If a stall is detected, the device will flag the fan as stalled and trigger an interrupt.
If the RPM-based Fan Speed Control Algorithm is enabled, the algorithm will automatically attempt to
restart the fan until it detects a valid tachometer level or is disabled.
The FAN_STALL Status bit indicates that a stalled fan was detected. This bit is checked conditionally
depending on the mode of operation.
Tachometer Measurement
Refer to
ranges (500, 1k, 2k, 4k).
device is put into Direct Setting and the fan drive is set at a level that is lower than the fan
can operate (including zero drive), then the tachometer measurement may signal a Stalled
Fan condition and assert an interrupt.
AN17.4 RPM to TACH Counts Conversion
Table
5.12).
DATASHEET
19
for examples and tables for supported RPM
Revision 1.2 (03-22-10)